This invention relates to fcc metals, or metals having a face-centered cubic lattice, which are controlled in crystal orientation to be suitable for use as target materials. The invention also relates to a process for producing such fcc metals.
With the recent development of the electronic industry, the use of sputtering target materials has increased and there is also a demand for improving their characteristics.
To provide metallization films on substrate wafers by sputtering, fcc metals are conventionally employed and required to have the following characteristics.
(1) They should have controlled specific crystal orientations, which depend on the property to be possessed by the fcc metal to be sputtered: PA1 (2) The fcc metal should also have good electromigration characteristics. As the line width of metallization or conductor films formed by sputtering on substrate wafers decreases, electromigration which is a kind of "breaking of wire" phenomenon has become a problem. It has been established that the phenomenon of electromigration is largely affected by the composition of the sputter film and, therefore, sputtering target materials which determine the compositions of sputter films in an almost unique way should also have good electromigration characteristics. PA1 (3) The fcc metal should have minimum levels of impurities. The reliability of conductors formed of sputter films is largely affected by their microstructure which, in turn, is largely affected by impurities including gaseous components. It is therefore desired that sputtering target materials should also have minimum levels of impurities other than specified components. PA1 (4) The fcc metal should have fine average crystal grain sizes. In order to enhance the uniformity of sputter films, as well as to improve the sputtering rate and directivity, it is desired that sputtering target materials have fine average crystal grain sizes. PA1 (1) In order to assure uniformity in sputter films, the fcc metals for use as sputtering target materials have desirably random orientations, which are evaluated by the integral intensities of (200) and (220) faces as relative to the integral intensity of a (111) face as measured by X-ray diffractiometry. If I.sub.(200) /I.sub.(111) is greater than 2.3 or if I.sub.(220) /I.sub.(111) is greater than 1.0, the orientations of crystal faces of the fcc metal cannot be regarded as being "random" and the film produced by sputtering will be deteriorated in uniformity. Therefore, the fcc metal that can be sputtered to produce a uniform film should satisfy the following relations: I.sub.(200) /I.sub.(111).ltoreq.2.3 and I.sub.(200) /I.sub.(111).ltoreq.1.0. PA1 (2) In order to assure high directivity in sputtering, the fcc metals for use as sputtering target material have desirably a dominant (110) orientation, which is evaluated by the integral intensities of (220) face as relative to that of a (111) face as measured by X-ray diffractiometry. If I.sub.(220) /I.sub.(111) smaller than 2.0, the (110) orientation cannot be regarded as being "dominant" and the directivity in sputtering will deteriorate. Therefore, the fcc metal that can be sputtered with high directivity should satisfy the following relation: I.sub.(200) /I.sub.(111).gtoreq.2.0. PA1 (3) In order to assure high sputtering rate and uniformity in the sputter film, the fcc metals for use as sputtering target materials have desirably a dominant (100) orientation, which is evaluated by the integral intensity of a (200) face as relative to that of a (111) face as measured by X-ray diffractiometry. If I.sub.(200) /I.sub.(111) is smaller than 4.6, the (100) orientation cannot be regarded as being "dominant" and the sputtering rate will deteriorate. Therefore, the fcc metal that can be sputtered with high rate should satisfy the following relation: EQU I.sub.(200) /I.sub.(111).gtoreq.4.6. PA1 (1) In order to produce fcc metals having random orientations, it is necessary to perform a so-called full annealing which is accompanied by recrystallization. Particularly in the case where the matrix of fcc metals is composed of Cu, recrystallization will not proceed fully if the heat treatment is performed at temperatures lower than 493 K or for periods shorter than 60 seconds. On the other hand, if the heat treatment is performed at temperatures higher than 823 K or for periods longer than 7,200 seconds, not only diseconomy but also coarse crystal grains will occur. Therefore, the heat treatment should be performed at a temperature of 493-823 K for a period of 60-7,200 seconds in order to produce a fcc metal having random orientations. PA1 (2) In order to produce fcc metals having a dominant (110) orientation, it is necessary to perform so-called stress relief annealing which is not accompanied by recrystallization. Particularly in the case where the matrix of fcc metals is composed of Cu, satisfactory stress relief is not accomplished if the heat treatment is performed at temperatures lower than 348 K or for periods shorter than 300 seconds. On the other hand, if the heat treatment is performed at temperatures higher than 473 K or for periods longer than 36,000 seconds, not only diseconomy but also recrystallization will occur. Therefore, the heat treatment should be performed at a temperature of 348-473 K for a period of 300-36,000 seconds in order to produce a fcc metal having a dominant (110) orientation. PA1 (3) In order to produce fcc metals having a dominant (100) orientation, it is necessary to perform a so-called full annealing which is accompanied by recrystallization. Particularly in the case where the matrix of fcc metals is composed of Cu, recrystallization will not proceed fully if the heat treatment is performed at temperatures lower than 493 K or for periods shorter than 60 seconds. On the other hand, if the heat treatment is performed at temperatures higher than 823 K or for periods longer than 7,200 seconds, not only diseconomy but also coarse crystal grains will occur. Therefore, the heat treatment should be performed at a temperature of 493-823 K for a period of 60-7,200 seconds in order to produce a fcc metal having a dominant (100) orientation. PA1 (1) In order to produce fcc metals having random orientations, it is necessary to perform cross rolling. If the total offset of the rolling axis in cross rolling is less than 90.degree., the aggregation of the (100) faces becomes unduly great; on the other hand, if the total draft that is achieved in cross rolling is less than 20%, the aggregation of the (110) faces is unduly great and whichever the case, the desired random orientations are not achieved. In addition, if the offset of the rolling axis in each pass is less than 15.degree., the total number of passes that are necessary in the rolling operation will increase to an uneconomical level. Therefore, the final working necessary for producing a fcc metal having random orientations is a so-called cross rolling which is performed to achieve a total draft of at least 20%, with the rolling axis being offset at 15.degree. or more in each pass to a total offset of at least 90.degree.. PA1 (2) In order to produce fcc metals having a dominant (110) orientation, it is also necessary to perform cross rolling. If the total offset of the rolling axis in cross rolling is less than 90.degree. or if the total draft that is achieved in cross rolling is less than 20%, the aggregation of (110) faces becomes unduly small. In addition, if the offset of the rolling axis in each pass is less than 15.degree., the total number of passes that are necessary in the rolling operation will increase to an uneconomical level. Therefore, the final working necessary for producing a fcc metal having a dominant (110) orientation is so-called cross rolling which is performed to achieve a total draft of at least 20%, with the rolling axis being offset at 15.degree. or more in each pass to a total offset of at least 90.degree.. PA1 (3) In order to produce fcc metals having a dominant (100) orientation, it is necessary to perform one-way rolling. If the total offset of the rolling axis is 15.degree. or more or if the total draft that is achieved by the rolling operation is less than 20%, the aggregation of (100) faces becomes unduly small. Therefore, the final working necessary for producing a fcc metal having a dominant (100) orientation is one-way or reciprocal rolling which is performed to a total draft of at least 20%, with the offset of the rolling axis for all passes being to be less than .+-.15.degree..
(i) In order to assure uniformity in the sputter film, it is particularly desired that the fcc metal have random orientations; PA2 (ii) In order to assure high directivity in sputtering, it is particularly desired that the fcc metal be dominantly (110) oriented. PA2 (iii) In order to assure high sputtering rate and uniformity in the sputter film, it is particularly desired that the fcc metal be dominantly (100) oriented.
Aluminum and any other materials that have heretofore been used to form metallization films by sputtering on substrate wafers do not satisfy the required characteristics to the fullest extent.